1. Field of the Invention
This invention relates to a releasing agent for use in the casting operation using a die or dies. More particularly, the invention relates to a releasing agent for die casting which agent is excellent in thermal insulating property or heat retaining property and which agent is especially suitable for use in the low speed casting operation of long, large sized and complicated articles, in which the molten metal in a die is liable to be cooled and releasability is strictly required such as in the squeeze die casting of aluminum articles.
2. Description of the Prior Art
The low speed casting with a low injection speed can produce high-strength cast articles because the method is free from the gas entrainment into cast articles. Accordingly, such a casting method is widely employed in the production of aluminum parts and accessories for automobiles or the like in the recent trend of weight saving.
Most of conventional releasing agents used for die casting are graphite-base compositions. However, because the releasing agents of this kind make the working environment dirty with their inherent black color, many other white releasing agents are also used such as natural minerals of talc, sericite and pyrophyllite; and other white releasing agents of boron nitride, polytetrafluoroethylene (PTFE) and so forth.
The particles of these releasing agents are dispersed in an aqueous medium containing a dispersing agent, e.g., carboxymethyl cellulose (CMC) to form a coating composition and the composition is applied to the inside wall of the cavity of a die to form a coating film on the wall surface.
In the above-described conventional die casting method, when the temperature of a molten metal is lowered before the die is completely filled up with the molten metal, the running of molten metal is impeded and several defects such as wrinkles, cold shuts and flaws are caused to occur. Furthermore, in the casting of articles of long, large sized and complicated shape, the releasability is impaired by solidification shrinkage to cause distortion in cast articles, and in a worst case, the releasing of cast products becomes impossible.
Conventional die releasing agents are good in thermal conductivity, so that they can be used for casting small parts in simple shapes, which process is relatively free from the occurrence of defects in casting. However, the conventional releasing agents are not suitable for casting thin, complicated and large articles because several defects are caused to occur on account of misrun of molten metal.